PHEROMONES AND PHYSIOLOGICAL CHANGES CAUSED BY THE MALE EFFECT
The introduction of a sexually active breeder in a flock of goats is able to stimulate the sexual activities of females (Avdi et al, 2004).
The presence cause changes in female physiology and this acute response is called male effect and seems to depend mainly on olfactory signals from pheromones produced by the males through stimulation of androgens in association with behavioural stimuli generated mainly during courtship activity.
The characteristic scent from the bull, buck or ram comes from the sebaceous glands where it is produced and is directly related to the concentration of testosterone.
These substances are detected by the olfactory receptor neurons (ORN) capable of detecting volatile odours or vomeronasal receptor neurons (VRN) which detect pheromones molecules.
The initial interaction between males and females occurs by action and recognition of pheromones, which are chemicals transported by air and excreted through faeces or urine or by skin glands, perceived by the olfactory system and capable of causing behavioural and endocrine alterations (Rekwoot et a; 2001) as part of chemical communication (Castaneda et al; 2007).
In the male, during the detection of olfactory signals, chemical communication is evidenced by the Felmen response.
It is through these pheromone stimuli, the sight of the male and the physical contact with the male that promote the restoration of hormonal activity in the female, with the consequent manifestation of estrus.
The male effect is capable of altering the female physiology (Abi Sallum and Claus, 2005).
The presence of the male is perceived through the recognition of pheromones by the olfactory system, which transmits a signal to the medial nucleus of the amygdala and then is relayed to the hypothalamus which is the generator of Gonadotropin-releasing hormones pulses (Murata et al; 2009).
Consequently, there is an increase in the frequency and amplitude of pulsatile luteinizing hormone secretions, increasing from 2 to 3 times the number of pulses.
Thus, exposure of females to sexually active males promotes a rapid activation of luteinizing hormones secretions and a reduction in negative estradiol feedback on the pituitary-hypothalamic axis, culminating in the preovulatory Luteinizing hormone surge.
Generating an acute response (short-term response) followed by a chronic response( long-term) interaction (chanvallon et al; 2010).
(Sakamoto et al, 2013) suggests that the man target of pheromones in goats are the kisspeptin and Neurokinin B neurons found in the accurate nucleus.
Identified a volatile molecule 4 elhyloctanal, as the pheromone of the buck responsible for the “Male effect” in goat reproduction.
This is the first report of the identification of a pheromone in mammals with clear evidence of regulation of reproduction.
MALE EFFECT AND INCREASED FREQUENCY OF GONADOTROPIN RELEASING LUTEINIZING HORMONE
In ruminants cattle, sheep and goats etc exposure of females to sexually active males during anestrous periods results in the activation and secretion of luteinizing hormones, the substance responsible for ovulation (Gele and Fabre-NYS 2004).
This rapid response, generating a higher frequency of luteinizing hormones pulses and concentration, increases significantly after exposure to male and tends to increase progressively over time (Martin et al, 1986).
This increase in luteinizing hormone concentration seems to be widespread, thus, it is verified an increase in all respects, either at the basal level or in the medium and maximum concentration of progesterone (Claus et al, 1990).
Bucks are capable of inducing estrus in cyclic females, but this factor is regulated by progesterone, thus does either early or late luteal phase is susceptible to these alterations.
But in females which have progesterone plasma levels higher than 5ng/ml, the male effect may have a low efficacy.
This fact is different in Ewes as these animals for having a shorter estrus cycle, have insufficient levels of progesterone to block the male effect.
After the introduction of males, follicle growth is pronounced reaching 1.5mm per day.
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